1. Field of the Invention
The present invention relates to a reinforcement material and, more particularly, to a synthetic fiber material for providing both structural and crack-controlling reinforcement to building materials.
2. Description of the Background of the Invention
It is well known that the addition of a reinforcement component to building materials such as cementitious materials, brick, asphalt, and the like improves the structural integrity of the material and reduces the likelihood of cracking. When incorporated into cementitious materials such as concrete, for example, the reinforcement component is added to reduce the effect of two main structural deficiencies: 1) low tensile strength; and 2) low strain at fracture. The tensile strength of concrete is relatively low because concrete, when formed, normally contains numerous micro-cracks. It is the rapid propagation of these micro-cracks under applied stress that is responsible for the low tensile strength of the material. Because of the widespread use and applicability of concrete, considerable research has been undertaken to lessen the effects of its deficient structural properties.
Typical reinforcement materials that are added to cementitious materials include, for example, various gauges of wire mesh or reinforcement fibers. A variety of reinforcement fiber additives are known in the art that provide strength characteristics to building materials. Typical reinforcement fibers include asbestos fibers, glass fibers, steel fibers, mineral fibers, and cellulose fibers. Some reinforcement fibers are better suited for particular applications than others. For example, asbestos fibers are known to provide effective reinforcement but, due to environmental and health concerns, are not extensively used. In addition, glass fibers and steel fibers are relatively expensive, and have a tendency to decompose in cementitious materials. Steel fibers typically decompose at the surface of the fiber reinforced material, whereas glass fibers continuously undergo decomposition as a result of the alkaline nature of cement. Also, due to the physical and chemical characteristics of steel fibers, there is some difficulty in uniformly distributing the steel fiber throughout the mixture. Furthermore, there are certain physical and operational deficiencies inherent with steel fiber that reduce its effectiveness. Such deficiencies include, for example, rebound in air-placed concrete applications, and relatively high equipment costs due to equipment wear from contact with the steel fibers.
It is known that concrete has a tendency to shrink after it has been cast due to the evaporation of excess mixing water. Plastic shrinkage causes the formation of shrinkage cracks shortly after the casting of the concrete, that weakens the matrix thereof. Unlike other fibrous materials, synthetic fibers are known to reduce such cracking caused by early plastic shrinkage. For example, a fibrillated fiber formed from a polyolefin film has been successfully used to prevent or reduce cracking. The fibers are stretched multiple times and then cut along lines at least partially transverse to the direction of orientation. The fibers are thereby fibrillated. When mixed within cementitious materials, in such a manner that they provide deformations to improve anchoring and bonding within the concrete matrix, the cut fibers are dispersed through the mixture, open to form webs nets, and thereby improve the strength and binding characteristics of the cementitious matrix.
Some advances have been made in the area of fiber reinforcement to provide increased toughness and durability, and reduce cracking in the matrix of building materials, such as concrete. However, the prior art reinforced fibers have a number of disadvantages that weaken or, otherwise, limit their effectiveness. Accordingly, there is a need for an improved reinforcement fiber that imparts improved structural properties to the building materials to which they are added. In particular, the need exists for a synthetic reinforcement fiber that when added to, for example, cementitious materials, provides a building material that exhibits reduced permeability, increased fatigue strength, improved toughness, and reduced plastic shrinkage.